Hi
as you all probably know im experiencing problems with my jaguar,
can old coils and spark plugs affect performance?

i have ngk bcpr6e spark plugs and old coils, maybe replacing should help? anyway, what spark plugs i should use on 4.0l 1998 xj8? aj27
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Sure can. If the electrode shrinks/wears or the gap is too large, it will affect performance, as the spark wouldn't be in the correct position. The same as coils. If they are old and worn, the generated spark can be very weak. Just enough to ignite the mix if not with the proper force/power.

Check the plugs as well as well for their colour. Black means too rich. White means too lean. Both will cause a lack of performance. They should be a light milk chocolate colour.

 

passenger side cylinders- spark plugs are chocolate color, as it should be.

Drivers side - spark plugs are white color. ,also same side catalyst converter is destroyed, looks like melted, just few hours ago i have removed exhaust and cleaned what left of it, few small pieces. .other side catalyst converter looks okay

 

but as understand second o2 sensor should trow trouble code, because catalyst converter is destroyed, but so far nothing. no trouble codes shows up

 

The sond can be dead too. White is too lean. So either too much air or too little fuel...

 

Have you considered using a ELM327 tool to get you the sensor information as it is running and recording , 12 bucks Ebay ?

O2 sensor code flag latching can be fickle .

See all of this video , but this is a lame example of software options:

 

sad news so far , today few new parts arrived expect spark plugs ...... new coils replaced, new MAF replaced and guess what ? waste of money , no changes at all, Monday new NGK BKR5EIX-11 spark plugs should arrive , HOPE new spark plugs will help because now i use totally wrong plus ngk bcpr6e

 

What are your symptoms? how is the car running? It sounds like an unmetered air leak if your engine destroyed a CAT. Running hot on one side?
Tests can be done by using a can of engine starter around the maf connections, along the induction tube (particularly the corrugated section, they crack) the throttle body and around the plenum, you're looking for a rise in engine revs as the leak sucks in the gas and the engine burns it.
It's work slowly with little puffs from the can, not blasting gas everywhere.

 

yes car is running well, just throttle response is very slow , i have checked all, no air leaks, just little hesitation on acceleration sometimes , very rarely

HOPE new spark plugs will help

 

Don't forget to check plug gap, I found I had to gap my plugs a bit (carefully) when I bought those same plugs you are getting. See post 5 here https://www.jaguarforums.com/forum/x...8/#post1773939

IIRC the plugs arrived with a 0.04 inch gap, where the table called for a .05 for my car.

If yours is a 98 it's probably not going to have an AJ27, it will have an AJ26 unless it has been swapped. In your case you should also need the .05 inch gap.

 

no , mine IS aj27 with VVT solenoids, was with nikasil linings , but last owner swaped engine from 2001 , so mine is 1998 jag and not even with nikasil linings

 

Then you may be able to get away without gapping the plugs, I'd check the gap on all of them just to be safe but I think they came out of the box with the right gap for AJ27 engines.

 

have you experienced some slow throttle response wit incorrect plugs ?

 

If I had to guess then I'd think there is something more going on than just bad plugs, but it's a little out of my experience to say for sure... If only the plugs on one bank looked fouled then I'd look at causes that would be common to all cylinders on that side. Maybe too lean a burn is what caused the cat to melt? Check the livedata and report back on OBD error codes, as well as the STFT and LTFT trims reported for each bank.

 

Neihh, the only solution is to throw more parts at it ... with several forum threads on this issue, and without any attempt to locate / isolate the problem ....

Sorry I am cynical here, but this goes nowhere.
I am very well aware these can be very complex problems, and I have been more than once corrected by this very same forum.

But, in order for us to help, you will really need to take a systematic approach to this.
Otherwise it will lead you to nothing, just a lot of frustrations, and an empty pocket at the end.

Get the basics done first with a OBD2 module and reader (a smart phone works perfect).
Get the codes stored, then delete them, drive around, and see what comes back.
Also set up some live readings for ignition advance, Short Term, and Long Term fuel trims.
In stead of speculating, you will get firm figures what is happening instead.

Then, keep it all in one thread, and go from there.

 

i know. . but i have another problems with obd connection. sometimes it connects sometimes not, when connecting to car ecu i have turn off the ignition and then instantly turn on again, then reader connects to ecu, i can see all the data all is fine, but after 2-20mins connection is lost again and i have to turn off and turn on ignition again

 

i have made video of fuel trims , are they normal? driving 60mph, then slow acceleration and deceleration , , at the end of the video connection to ECU has been lost as always, i need to stop, turn off and on ignition, then readings comebacks